EP-B-0,008,398 has disclosed a process for decaffeinating coffee, wherein caffeine is extracted from raw coffee by an aqueous fluid. The extraction fluid is passed over a preloaded activated carbon adsorber, the caffeine being adsorbed.
Since the raw coffee is delivered usually has a water content of 7 to 15 g of water/100 g of dry matter, it absorbs water in an aqueous fluid. During this swelling process, up to 160 g of water/100 g of dry matter (usually 130 g of water/100 g of dry matter) can be additionally absorbed by the raw coffee bean, the volume of the raw coffee bean being approximately doubled. In order then to avoid blocking of the column apparatus, which is used normally for taking the raw coffee beans, the dumped charge is kept moving during the swelling process by special measures (fluidizing with water or preswelling in a mechanical mixer). During this movement of the beans, however, fine particles are detached from the surface of the beans (silvery pellicle), which particles are carried along by the fluid and cause blockage in the downstream activated carbon adsorber.